Medtronic Guardian 3: “Do Not Calibrate. Sensor Updating…” Error

Medtronic 670G Insulin Pump with "Do not calibrate. Sensor Updating" Message

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Living with diabetes has taught me a lot of life lessons. One of them is that most things we can’t control.

There is some irony in this post, as I recently wrote a blog post about how I like to start my Guardian CGM sensor on Sunday. Well, my sensor failed early and I had to start a new one on Saturday this week. The Guardian 3 CGM sensors are supposed to last 7 days but technology is imperfect and sometimes they fail early. This is actually the first time I’ve experienced this in the 8 months I’ve been using the Medtronic 670G Insulin Pump system, so I wouldn’t say that this is a common issue, but certainly something you’re likely to come across at some point.

What does “Sensor Updating” mean?

According to the Medtronic Minimed Insulin Pump 670G Auto mode FAQ webpage, this sensor updating alert means that “Your pump is performing checks to see if sensor values are reliable,” and you should follow your pump’s instructions.

If you participate in diabetes discussion forums or have spent much time reading on the internet, then you’ve probably come across people talking about the error message “Do not calibrate. Sensor Updating. ” From the anecdotes that I’ve read, it seems likely that the sensor will fail. If it fails, you will see a “Change sensor” message. However, the “Sensor updating” alert can stay on for 3 hours and does not mean failure will definitely happen.

You can wait to see if the sensor starts working again, or you can change the sensor as a precaution.

Get a replacement senor

If you want to get a replacement sensor from Medtronic due to the “Sensor updating” alert, it’s probably best to wait the 3 hours to see if the sensor fails, since “Did the sensor updating message last longer than 3 hours?” is one of the questions on their sensor replacement form.

There is an online sensor replacement form available, that can be used to request a free replacement in some cases. Below are the links to the form for USA and Canadian residents. If the form doesn’t work, then call Medtronic to request a replacement. You can find their phone number on the bottom of your insulin pump.

I have called Medtronic in the past and they are very good about sending out a replacement sensor. I once had a sensor that didn’t work at all (starting from day 1, I was unable to calibrate and got the change sensor message), and they sent a replacement sensor. It’s a good idea to save the piece of paper that has the sensor lot number on it, so that you can report the lot number when it fails. However, that is not required to get a replacement.

When the sensor is updating, the sensor does not display a glucose number. The insulin pump, if in auto mode, may switch to Safe Basal mode.

Be prepared for sensor failure

In my experience, sensor failure before 7 days is uncommon. However, it’s definitely a possibility. For me, having a sensor fail unexpectedly can be a major disruption, as I use auto mode. Without a sensor, the pump will switch into manual mode. Since there is no sensor reading, manual mode will continue to give the programmed basal rate, and the pump doesn’t know if the blood glucose is dropping too low.

I personally stay prepared for sensor failure by always carrying a glucose meter with me. That way, I can test my blood glucose and adjust my basal rate up or down depending on if I’m trending low or high. This requires more work on my part, and makes me somewhat anxious. But, at least it’s a back up plan. It’s better than no plan.


  1. The information was very helpful. However, I have gone through 5:consecutive sensor failures. Has this happened to anyone else? Medtronics is sending me replacement sensors.

    • We are up to our 11 consecutive early sensor failure. Each has been replaced but having to call the helpline and going through the same troubleshooting is driving us crazy. We had no problems for the first 4 months of use and the last month has been a nightmare.

    • YES!!! I’m so frustrated. Medtronic is sending replacements but it only seems to be lasting me about 4 days!! I don’t know what the problem is, Medtronic doesn’t know either.

  2. I never had trouble with my sensor with my 670G pump but since I got my 770G I have had trouble after trouble with my sensors. I even had my Medtronic trainer retrain me on the sensor and she put a new one on me and now I’m 5 days out and it’s messing up again.

  3. This is a very common issue on the Medtronic 670G. About 1 in 5 sensors stop early for me. Save the wrapper and they will replace them. Up to 3 in 90 days.

  4. I upgraded from the 670G to the 770G, now using the G3 sensors and transmitter. I am getting many of these “Do Not Calibrate. Sensor Updating” errors, and today had an error, a recovery and less than 5 minutes later the same error occurred. The second time the sensor did recover for about and hour but I got a third Do Not Calibrate.Sensor Updating which did not recover and I got the replace sensor message. My trainer has also checked me out and cannot figure out the reason. This is frustrating especially as I upgraded to the 770G hoping to avoid the same problem that I was having with the old sensors and the 670G pump.

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